It initiates the request to the second user agent server (UAS-2) after getting a successful response from the first server.

从第一个服务器成功获取响应之后，启动对第二个用户代理服务器(UAS - 2)的请求。

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Unlike a proxy that forwards on the requests, a B2BUA acts as both a user agent server (UAS) and a user agent client (UAC) to further participate in the SIP transaction.

与转发请求的代理不同，B2BUA 同时充当进一步参与 SIP 事务的用户代理服务器 (UAS) 和用户代理客户机 (UAC)。

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